Flow assisted catheter

ABSTRACT

A catheter includes a manifold and a proximal shaft portion coupled to the manifold. A distal shaft portion is coupled to a distal end of the proximal shaft portion and is flexible relative to the proximal shaft portion. A fiber reinforcement layer is disposed about the distal shaft portion.

REFERENCE TO CO-PENDING APPLICATION

The present application is a continuation application of U.S. patentapplication Ser. No. 09/181,848, filed Oct. 28, 1998 now U.S. Pat. No.5,961,511 entitled “CATHETER HAVING LCP REINFORCED DISTAL PORTION”.

BACKGROUND OF THE INVENTION

The present invention deals with medical tubes. More particularly, thepresent invention deals with medical tubes, such as catheters.

Flow directed or flow assisted catheters are catheters which are used toaccess extremely tortuous vasculature, such as neuro vasculature.Conventional, over-the-wire catheters can also be used, but exhibitlimitations in their ability to reach and maneuver within such intricatevasculature. Therefore, the flow assisted catheter is used.

Flow assisted catheters typically have a distal portion which isextremely flexible. Some flow assisted catheters also typically have aninflatable balloon or bulbous member at their distal ends. The flowassisted catheter is inserted into a vessel to be accessed through aguide catheter, and fluid may typically be pulsed through the guidecatheter to carry the flow assisted catheter into the desired vessel.Once in the vessel, the flow assisted catheter is drawn through thevessel (primarily by blood flow) and is fed into the vessel by thephysician. If the catheter has a balloon, the balloon is inflated toincrease the drag between the blood flowing in the vessel and the distalend of the flow assisted catheter. The balloon is essentially carried bythe flow through the vasculature to a target site. This draws thecatheter along to the target site.

If the distal tip of the catheter becomes frictionally engaged with avessel wall, or becomes “hung up” at a vessel branch, slack develops inthe catheter. The physician then slightly withdraws the catheter untilthe catheter has moved away from the vessel wall or branch and is againfree to move within the vessel. Once flow has taken up all the slack,the physician then feeds additional catheter length into the vessel.

In addition, some prior flow directed catheters included bent (typicallysteam formed) tips at the distal end of the flow directed catheter. Thishas been done in an effort to provide some selective tracking of theflow directed catheter into a desired vessel branch.

Current flow directed catheters suffer from a number of disadvantages.The distal portion of the flow directed catheter must be extremelyflexible so that it is capable of tracking the intricate vasculature tothe site to be accessed under the influence of flow in the vessel.Consequently, conventional flow directed catheters have had distalportions formed of material which is extremely flexible, and which isalso quite soft. Typically, the softer the material, the lower the burstpressure. Thus, some conventional flow assisted catheters are formedwith distal shaft portions with undesirably low burst pressure. This cancause the catheter to burst when injectate is introduced through thecatheter.

Further, soft materials commonly have undesirably low tensile strengthand also tend to stick to the vessel wall. This can cause the catheterto hang up in the vessel more often. When withdrawing the catheter todisengage it from the vessel wall, or when removing the catheter fromtortuous vasculature, a catheter with such low tensile strength issusceptible to breakage.

In addition, when the physician is feeding the catheter into the vessel,the highly flexible distal portion of the conventional flow directedcatheter can accumulate slack and loop. Then, when the treatingphysician withdraws the flow directed catheter, it can easily kink.

Further, the flexible nature of the distal portion of conventional flowdirected catheters makes it virtually non-torquable by the treatingphysician. In other words, if the treating physician rotates or torquesthe proximal end of the flow directed catheter, the distal portion ofthe flow directed catheter is so flexible, and has such low torsionalrigidity, that the torque does not transfer to the distal end. Thephysician must over-rotate the proximal end of the catheter, withdrawthe catheter a short distance, allow the catheter to advance in thevessel and hope for some unpredictable amount of torque at its distalend. This makes selective tracking very difficult and cumbersome, evenwhen the catheter includes a shaped tip.

The inability to transfer torque, in itself, leads to anothersignificant problem as well. When the flow directed catheter hangs up inthe vessel, the attending physician cannot break the friction betweenthe catheter and the vessel wall by simply torquing the catheter.Rather, as described above, the physician must withdraw the flowdirected catheter to some extent so it disengages from the vessel wall.Repeatedly withdrawing and advancing the flow directed catheter causesthe treating physician to take an undesirable amount of time inaccessing the target vasculature.

Also, in order to make the catheters highly flexible, they are oftenmade with a very small diameter. This results in very low flow rates ofinjectate through the catheter and also makes it particularly difficult,if not impossible, to use such catheters to deliver large particles orcoils. Finally, the soft materials used with such catheters are nottypically compatible with some agents, such as alcohol. This isundesirable since a physician may wish to deliver alcohol with such acatheter.

SUMMARY OF THE INVENTION

A catheter includes a manifold and a proximal shaft portion coupled tothe manifold. A distal shaft portion is coupled to a distal end of theproximal shaft portion and is flexible relative to the proximal shaftportion. A fiber reinforcement layer is disposed about the distal shaftportion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a side view of a flow directed catheter according to thepresent invention.

FIGS. 1B and 1C are cross-sectional views of the catheter shown in FIG.1.

FIG. 2A is a side view of a portion of a braid according to the presentinvention.

FIG. 2B is a cross-sectional view of the braid shown in FIG. 2A.

FIG. 3A is a side view of a second embodiment of a flow directedcatheter according to the present invention.

FIGS. 3B, 3C, 3D, 3E, 3F and 3G are cross-sectional views of thecatheter shown in FIG. 3A.

FIG. 4 illustrates one embodiment of a tip portion of a catheteraccording to the present invention.

FIG. 5 shows a second embodiment of a tip portion of a catheteraccording to the present invention.

FIG. 6 shows a third embodiment of a tip portion of a catheter accordingto the present invention.

FIG. 7 is another embodiment of a tip portion of a catheter according tothe present invention.

FIG. 8 is another embodiment of a tip portion of a catheter according tothe present invention.

FIG. 8A shows another embodiment of a tip portion of a catheteraccording to the present invention.

FIG. 8B shows a contoured surface of a catheter according to the presentinvention.

FIGS. 9A and 9B show a portion of a conventional braiding machine.

FIG. 9C illustrates a modified assembly mounted on the braiding machineshown in FIGS. 9A and 9B.

FIGS. 10A-10C illustrate a plurality of other embodiments implementingfeatures of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1A is a side view of one preferred embodiment of a flow directedcatheter 10 according to the present invention. Catheter 10 includesmanifold 12 and shaft 14. Shaft 14 includes proximal shaft portion 16and distal shaft portion 18. Distal shaft portion 18, has, at its distalend, tip 20. Catheter 10 also includes marker band 22 which is formed ofradiopaque material that can be observed under fluoroscopy.

In a preferred embodiment, catheter 10, from manifold 12 to tip 20 isroughly 100-200 cm in length. In addition, distal shaft portion 18 ispreferably approximately 45 cm to 55 cm in length.

Proximal shaft portion 16 is formed to be rigid relative to distal shaftportion 18. Distal shaft portion 18, on the other hand, is extremelyflexible and suitable for being assisted or directed through a vessel inthe human body by blood flow. Bulbous tip 20 is provided to increase thedrag between the blood flowing in the vessel and catheter 10. Whilecatheter 10 can be used without tip 20, the increased drag provided bytip 20 allows the blood flow to assist in tracking the catheter to thevascular site to be accessed.

It is also desirable (although not necessary) that proximal shaft 16have relatively high torsional rigidity so that it transmits a largeportion of torque applied by the administering physician to distal shaftportion 18. Also, it is preferred that proximal shaft portion 16 berelatively stiff or rigid in the axial direction so that the treatingphysician can insert shaft portion 16 into a guide catheter simply bypushing on shaft portion 16.

It is important that distal shaft portion 18 be extremely flexible sothat it can be carried through tortuous vasculature. However, it is alsovery important that distal shaft portion 18 be strong in both tensilestrength and burst strength. Further, it is desirable that distal shaftportion 18 have relatively high torsional rigidity (also referred to astorsional stiffness) to transmit torque applied by a treating physicianthrough manifold 12 or proximal shaft portion 16.

FIG. 1B is a cross-section of shaft portion 16 taken along section lines1B—1B in FIG. 1A. The outer diameter of proximal shaft portion 16 isapproximately 2.8 French. FIG. 1B shows that proximal shaft portion 16is formed of a number of layers Proximal shaft portion 16 has anundercoat layer 24 which defines the inner lumen of catheter 10.Undercoat layer 24 is preferably urethane, PVC, polyamide, or silicon.Proximal shaft portion 16 also includes a reinforcement layer shown inFIG. 1B as braid layer 26. The braid layer 26 is described in moredetail with respect to FIGS. 2A and 2B. Briefly, however, braid layer 26is formed of fibers braided about layer 24 to add strength to, andincrease the torsional rigidity of, proximal shaft portion 16. Afterbraid layer 26 is disposed about layer 24, overcoat layer 28, similar tolayer 24, is coated onto braid layer 26. Layer 28 is also formed ofurethane, PVC, polyamide, or silicon. Finally, a stiff jacketing layer30 is provided over layer 28. Stiff jacketing layer 30 is formed ofrelatively stiff material (e.g., having an elastic modulus greater than10,000 psi) such as polyimide, PVC, polyethylene or PET. Such aconfiguration provides proximal shaft portion 16 with a relatively stiffor rigid characteristic, and with a high degree of strength.

FIG. 1C is a cross-section of distal shaft portion 18 taken alongsection lines 1C—1C in FIG. 1A. FIG. 1C shows that distal shaft portion18 is preferably formed of undercoat layer 24, braid layer 26 andovercoat layer 28 shown in FIG. 1B, which simply extend continuouslyfrom within stiff jacketing layer 30. In this way, distal shaft portion18 is highly flexible, yet the braid layer 26 provides distal shaftportion 18 with very high burst pressure, tensile strength and torsionalrigidity.

FIG. 2A illustrates a portion of braid layer 26 in greater detail. FIG.2A illustrates that braid layer 26 is formed of a number of differentfibers 32, each fiber comprising a plurality of individual filaments 34.In the preferred embodiment, braid layer 26 is formed of eight fibers32, each comprising five filaments 34. Further, in one preferredembodiment, the filaments 34 are formed of a liquid crystal polymermaterial, such as a material commercially designated as Vectran sold byHoechst Celanese Corporation of Charlotte, N.C. The filaments 34 areeach approximately 20-25 microns in diameter. Five filaments 34 areassembled together to preferably form one 25 Denier fiber 32.

FIG. 2A also shows that, in braid layer 26, the fibers 32 overlap oneanother at areas referred to as picks 36. The number of picks perlongitudinal inch of catheter 10 affect both the burst strength andtorsional stiffness of catheter 10. In the preferred embodiment, braidlayer 26 has approximately 70-120 picks per longitudinal inch of thecatheter.

FIG. 2B is a cross-section of the portion of catheter 10 shown in FIG.2A and taken along section lines 2B—2B in FIG. 2A. FIG. 2B shows layers24, 26 and 28 in greater detail. In the preferred embodiment, layers 24and 28 are formed of a product commercially designated as Desmopan soldby the Polymers Division of Miles Inc. which is located in Pittsburgh,Pa.

FIG. 2B also better illustrates the process of making catheter 10. FIG.2B shows a copper mandrel or copper core 38 disposed within the innerlumen of catheter 10. In the preferred embodiment, undercoat layer 24 isextruded onto copper mandrel 38. Braid layer 26 is applied to layer 24and that entire assembly is encased in overcoat layer 28 which isextruded over braid layer 26. To remove mandrel 38, the axial ends ofmandrel 38 are pulled in opposite directions. This causes mandrel 38 toneck down to a smaller diameter and break free of undercoat layer 24.Once free, mandrel 38 is removed. On proximal shaft portion 16, stiffjacketing layer 30 is then placed over layer 28 to provide the desiredstiffness. In order to place layer 30 over layer 28, the axial ends ofthe braided shaft are pulled in opposite directions. This causes thebraid layer 26 to decrease in diameter. Jacketing layer 30 is thenplaced over braid layer 26 and the ends of the braid are released. Thiscauses the braided shaft to increase in diameter frictionally engagingjacketing layer 30. Both ends of jacketing layer 30 are then bonded tolayer 28.

In another embodiment, layers 28 and 30 are coextruded on braid layer26. The coextrusion runs substantially the entire length of thecatheter. After the catheter has been cut to an appropriate length, theouter, stiffer layer 30 is removed from the distal portion of thecatheter by grinding, scraping, or other suitable means. Thus, thecatheter has a stiffer proximal portion and a more flexible distalportion with one continuous inner lumen. Manifold 12 is assembled ontoproximal shaft portion 16 in any suitable, known manner.

The extrusion process used in forming the present invention preferablyutilizes the above-described over core extrusion technique. The corematerial utilized for the shaft according to the present invention ispreferably an annealed copper. The core may be preheated prior to thefirst extrusion pass. Preheating prior to the second extrusion pass mayalso be used to possibly improve adhesion between the layers.

FIG. 3A is a preferred embodiment of a catheter 40 according to thepresent invention. Catheter 40 includes manifold 42, proximal shaftportion 44, midshaft portion 46, distal shaft portion 48 and flexibletip portion 50. Flexible tip portion 50 is also provided with aradiopaque marker band 52 which is visible under fluoroscopy. As withcatheter 10, catheter 40 is preferably approximately 160-165 cm inlength from manifold 42 to marker band 52. Also, midshaft portion 46 anddistal shaft portion 48, along with flexible tip portion 50, areapproximately 45 cm to 55 cm in total length. The particular length ofmidshaft portion 46 and distal shaft portion 48 will vary depending onthe particular application in which catheter 40 is used.

In the preferred embodiment, proximal shaft portion 44 is relativelyrigid or stiff, midshaft portion 46 is a transition portion which ismore flexible than proximal shaft portion 44, but less flexible thandistal shaft portion 48. Distal shaft portion 48 is highly flexible,similar to distal shaft portion 10 of catheter 10 shown in FIG. 1A.Flexible tip portion 50 has even greater flexibility than distal shaftportion 48.

FIG. 3B is a cross-sectional view of catheter 40 taken along sectionlines 3B—3B in FIG. 3A. FIG. 3B shows that proximal shaft portion 44 isformed of a single, relatively stiff, material such as polyimide orpolyurethane. In the preferred embodiment, the outer diameter ofproximal shaft portion 44 is approximately 2.8 French.

FIG. 3C is a cross sectional view of catheter 40 taken along sectionlines 3C—3C in FIG. 3A. In the preferred embodiment, midshaft portion 46has an inner diameter in a range of approximately 0.010 inches to 0.022inches. Midshaft portion 46 preferably has approximately the same outerdiameter as proximal shaft portion 44.

FIG. 3C shows that midshaft portion 46 is substantially formed of fourlayers. Layers 54, 56 and 58 are similar to layers 24, 26 and 28 shownin FIGS. 1B and 1C. In other words, an undercoat 54 of polyurethane(preferably Desmopan) is first extruded and then a braid layer 56(preferably formed of strands of Vectran fiber) is braided onto layer54. Then, an overcoat layer 58 (also preferably of polyurethane orDesmopan) is extruded over braid layer 56. FIG. 3C also shows thatmidshaft portion 46 has an outer layer 60 which provides midshaftportion 46 with a stiffness that is preferably intermediate that ofproximal shaft portion 44 and distal shaft portion 48. Outer layer 60,in the preferred embodiment, is a polyurethane material commerciallydesignated as Texin 5286 (or other suitable material) which is necked ordrawn over layer 58. In other words, layer 60 is placed over layer 58and drawn through a heated die. In another embodiment, layer 60 is firstswelled, then placed over layer 58 and then shrunk to fit over layer 58.Texin is commercially available from the Polymers Division of Miles Inc.of Pittsburgh, Pa.

In another preferred embodiment, the layers of catheter 40 can be formedusing the coextrusion and grinding process described above with respectto catheter 10.

FIG. 3D is a detailed cross-sectional view of a joint portion 62 betweenproximal shaft portion 44 and midshaft portion 46. Midshaft portion 46has a proximal end 64 which includes only layers 54, 56 and 58 shown inFIG. 3C. In other words, outer layer 60 is removed. Distal end 68 ofproximal shaft portion 44 has a portion removed from the inner diameterthereof to form an enlarged receiving aperture. The inner diameter ofthe enlarged receiving aperture in end 68 of proximal shaft portion 44is sized just larger than the outer diameter of the proximal end portion64 of midshaft portion 46. Therefore, end 64 of midshaft portion 46 fitssnugly within end 68 of proximal shaft portion 44. Further, any suitableadhesive or fastening technique can be used to secure end 64 within end68.

FIG. 3E is another preferred embodiment of joint portion 62 joiningmidshaft portion 46 to proximal shaft portion 44. In the embodimentshown in FIG. 3E, proximal shaft portion 44 has a tapered distal end 70which reduces to a small outer diameter. Midshaft portion 46, bycontrast, has an expanded proximal end portion 72 which expands to havean inner diameter just larger than the outer diameter of tapered endportion 70 of proximal shaft portion 44. Tapered end portion 70 fitssnugly within the inner diameter of expanded end portion 72 and, as inthe embodiment shown in FIG. 3D, any suitable, commercially availableadhesive or fastening technique can be used to couple end 70 to end 72.

FIG. 3F is another preferred embodiment of joint portion 62 joiningmidshaft portion 46 to proximal shaft portion 44. In the embodimentshown in FIG. 3F, the proximal shaft portion 44 has a tapered distal end101 which reduces to a small outer diameter. The midshaft portion 46, bycontrast, has a notched, or slightly enlarged proximal end 99 which islarge enough to have an inner diameter just larger than the outerdiameter of tapered end portion 101 of the proximal shaft portion 44. Aradiopaque marker band 103 is placed over distal end 101 of proximalshaft portion 44. The manner in which radiopaque marker band 103 isplaced over proximal shaft portion 44 is described later in greaterdetail, with respect to FIG. 4. The marker band 103 is then covered witha urethane adhesive 105. The urethane adhesive 105 is then covered, inturn, by an epoxy adhesive 107 which underlies a polyimide sleeve 109.Sleeve 109 preferably extends through a major portion of joint portion62 and is adhered to joint portion 62 through epoxy adhesive 107. Aswith earlier embodiments, adhesives 105 and 107 are preferablycommercially available adhesives known in the art.

FIG. 3G is a cross-sectional view of distal shaft portion 48 taken alongsection lines 3G—3G in FIG. 3A. FIG. 3G shows that distal shaft portion48 is formed of only layers 54, 56 and 58. Therefore, distal shaftportion 48 is extremely flexible, yet has high tensile strength andburst strength.

FIG. 4 is a cross-sectional view of one embodiment of a distal tip 18′suitable for use with either catheter 10 shown in FIG. 1A or catheter 40shown in FIG. 3A. FIG. 4 shows that the tip portion is formed similarlyto the distal shaft portion 18 shown in FIG. 1C. Radiopaque marker band22 is provided at the very distal end of the shaft portion 18′ and, inthe embodiment shown in FIG. 4, the enlarged bulbous tip 20 is removed.

FIG. 5 shows a second embodiment of a distal tip 50′ suitable for use astip 50 shown in FIG. 3A.

FIG. 5 shows that tip portion 50′ has a tapered outer layer 58 to whichmarker band 52 is adhesively secured.

The length of tapered tip 50′ is, in one preferred embodiment,approximately 2-3 cm. Tip 50′ has tapered overcoat layer 58 to provideeven greater flexibility than the remainder of distal shaft portion 48.

FIG. 6 is a cross-sectional view of yet another embodiment of a distaltip 75 suitable for use with either catheter 10 or catheter 40. FIG. 6shows tip 75 attached to shaft portion 48 of catheter 40. In FIG. 6, ametal coil 70 (which is preferably formed of a radiopaque material suchas platinum) is secured to the distal end of distal shaft portion 48.Coil 70 is preferably formed of 0.001-0.002 inch platinum wire and istherefore radiopaque. Coil 70 is preferably encased by placing it onundercoat layer 54 and dipping coil 70 into dissolved encasing material.

FIG. 7 shows another embodiment of a distal tip of a catheter 10, 40according to the present invention. Tip 80 is preferably heat or steamshapeable, along with layers 26, 56. It should be noted that tip 80 caneither be integrally formed with catheter 10, 40 simply as the distalend thereof, or it can be formed separately and connected to catheter10, 40.

The curved shape improves tracking because tip 80 does not dive into theouter radius of a vessel bend as it approaches the bend. Rather, tip 80reaches the outer curvature of the bend and, when properly oriented bythe physician, slides along the bend. Bent tip 80 only provides thissignificant advantage if it can be oriented properly within the vessel.In conventional flow directed catheters, the torsional rigidity (andhence torque transfer) is very low and orientation of tip 80 was verydifficult. Since braided layers 26 and 56 are provided in catheters 10,40 according to the present invention, rotating the proximal shaftprovides a very predictable rotation at the distal portion of the shaft.This significantly increases selective tracking of the flow directedcatheter 10, 40 and improves catheter advancement.

Tip portion 80 also increases pressure drag within the vessel. In otherwords, since tip 80 is bent, the friction between tip 80 and the fluidflowing in the vessel is higher than if tip 80 were straight. Thisfurther assists in moving the catheter along the vessel.

It should be noted that tip 80 can also be provided in a spiral orsquiggle configuration to orient tip 80 into the axis of flow throughthe vessel thereby increasing drag by increasing the surface area of theshaft exposed to the flow.

FIG. 8 shows a second embodiment of a distal tip portion 83 of shaft 10or 40 according to the present invention which increases drag of thecatheter 10, 40 relative to fluid flowing in the vessel. A plurality ofbulbous or balloon members 82 are provided at the distal tip 83. Thisserves to increase the friction between the flowing fluid in the vesseland the catheter 10, 40. This further assists in catheter advancement.It should be noted that, as shown in FIG. 8A, either of the bulbousmembers 82, or additional bulbous members 82, can be attached to anextremely flexible thread 85 which is attached to, or run through, thecatheter 10, 40. Since thread 85 is even more flexible than the distalportion of the shaft, it assists in tracking through tortuousvasculature and essentially drags the distal tip of the catheter alongto the site to be accessed. Also, bulbous member 82 is preferably placeda short distance proximal of the distal tip of the catheter rather thanprecisely at the distal tip. For example, in the embodiment shown inFIG. 7, bulbous member 82 is preferably placed just proximal of the bendin tip 80. This placement aids in tracking by increasing drag, but doesnot significantly affect the ability of the distal tip to select smallvessels.

FIG. 8B shows yet another embodiment of the present invention utilizedto increase drag of the catheter relative to the flow in the vessel.FIG. 8B shows that a contoured shape is provided on the outer surface 84of the distal end portion of the shaft of catheters 10, 40. Such acontour can be cut or compressibly formed into the outer surface of theshaft using appropriate tooling. Further, such an impression can be madein the outer surface of the shaft utilizing molding techniques.

Braid layers 26 and 56 are preferably applied to extruded layer 54 withcommercially available braiding machines. Two such machines which havebeen used with satisfactory results are the Kokubun No. ST16 BraidingMachine commercially available from Toyota Tsusho America or KokubunLtd. from Hamatsu, Japan. A second commercially available system whichhas been used satisfactorily is one available from Wilhelm Steeger GmbH& Co. type no. K80/16-72/89 Braiding Machine. Wilhelm Steeger GmbH & Co.is located in Barmen, Germany.

Both machines are preferably somewhat modified in order to performsatisfactorily. The machines are typically designed to braid largergauge fibers than those used with the present invention. Themodifications to the machines for adaptation to the present inventionfocused on the carriers or totes that hold and dispense fiber as theycirculate around the inner hub or braid point.

It is important in braiding layers 26 and 56 to have low tension on thefiber and to minimize sliding contact with any parts on the braidingmachine which can damage the fibers. Minimizing damage and high tensionin the fiber is also important when the fiber is wound on the spools ofthe braider. Further, ionized air is used in the system in a knownmanner to control and remove undesirable foreign material during thebraiding process.

To better illustrate the modifications to both the Steeger and Kokubunmachines, the modifications to a Steeger machine will now be described.FIG. 9A is a schematic view of the operation of the conventional,unmodified, Steeger machine identified above. The fiber is removed froma storage mechanism 59, travels through a first eyelet 61 and isthreaded about a plurality of pulleys 63. The fiber is then threadedthrough a top eyelet 65 and then provided to the braid point or innerhub 90.

FIG. 9B is a side view of a portion of a standard Steeger fiber carrierused in the above-identified braiding machines. It will be noted thatthe Steeger machine provides a double pulley assembly with a top eyelet67 through which the fiber travels to the braid point 90. It has beenfound that eyelet 67 was a source of problems in that it damaged thefiber due to friction and due to surface roughness.

FIG. 9C is one embodiment of a top carrier assembly 70 used in modifyingboth the Kokubun and Steeger machines. The machine carriers areoriginally provided with the top eyelet which, as discussed above,caused damage to the fibers. Therefore, assembly 70 is mounted on thetop of the carriers to replace the eyelet. Assembly 70 includes mountingblock 72, pulley 74 and conical spool 76. Mounting block 72 is assembledonto the top 77 of the carrier (shown in FIG. 9B). Pulley 74 isrotatable about axis of rotation 78 and conical spool 76 is rotatableabout axis of rotation 80. The fiber 82 is threaded from the standardlower portion of the machine. However, instead of traveling througheyelet 67, the fiber travels up around pulley 74 and around conicalspool 76 and then to the braid point or central hub 90 on the machine.

In the Kokubun machines, the carriers are commonly of nearly all metalconstruction. A similar combination of eyelets and pulleys are used toguide the fiber through the machine and to control timing during whichmore fiber is released from a storage spool. However, the eyelets on theKokubun machine have also been observed to cause damage to the fibersfrom sliding friction, and breakage of the fibers from surfaceirregularities on the eyelet. Thus, the Kokubun machine was modified toreplace the eyelets with Delrin or Teflon plastic rollers.

Further, the Kokubun machine is provided with only a single pulleysystem (as opposed to the double pulley system shown on the Steegermachine). This was replaced with a pair of pulleys to reduce the tensionin the fiber. By replacing the metal contact portions with plasticparts, significant advantages are achieved. The parts move more quicklybecause they have smaller mass than the metal parts, and the plasticparts are not slowed down by lubricant which is required in metal partdesigns.

A spring (79 in FIG. 9B) is provided in the carriers of both Steeger andKokubun machines which provides the tension for fiber take-up. Thetake-up spring 79 must provide low enough force to keep tension as lowas possible on the fiber, but must be high enough to have a quickresponse as the carrier weaves in and out along its path around thebraid point 90. A preferred tension (the force measured to pull thefiber off of the carrier) is in a range of approximately 20-90 grams.

The pulleys provided with the Steeger machine had observable surfaceroughness. These pulleys were replaced with pulleys made from ultra highmolecular weight polyethylene.

The number of picks per inch provided by the braid, and the number ofelements in the braid, affect both flexibility and strength. In otherwords, the higher the pick count, the stronger the catheter (withrespect to both burst pressure and tensile strength), and the moretorsional rigidity is exhibited by the catheter.

FIGS. 10A-10C illustrate other embodiments of the present invention. InFIG. 10A, a cross section of a portion of a catheter 110 is shown.Catheter 110 has improved lumen characteristics in order to, forexample, deliver embolic materials. Catheter 110 has a shaft whichincludes a distal section 112 and a proximal section 114. Sections 112and 114 are connected by a transition point 116. Proximal section 112 isformed by extrusion of a stiffening layer 113, such as polyimide,polyamide, or polyurethane. Distal section 114 has an outer layer 115which is also extruded and is preferably a material which is moreflexible than layer 113 at proximal section 112. Outer layer 115 ispreferably formed of polyurethane. Transition point 116 defines aportion of catheter 110 in which the changeover in the extruder headfrom material comprising proximal section 112 to the material comprisingdistal section 114 occurs. Therefore, the material in transition point116 is a combination of those two materials.

Catheter 110 also includes a braid layer 118 which is similar to thatdescribed in the previous embodiments. Catheter 110 is also providedwith an inner lining 120. Inner lining 120 is preferably constructed ofa material which is lubricous and chemically resistent, such aspolytetraflouroethylene (PTFE), polyethylene (PE) or fluorinatedethylene polymer (FEP). This material provides a more lubricous layer toaid in guide wire insertion and manipulation, and it also aids in thepassage of solid embolic materials, such as platinum coils and PVAparticles. Because these tend to be relatively stiff material (i.e.,where the elastic modulus E is on the order of 30,000-120,000), thelayer must be thin so as not to make the shaft of the catheter toostiff. Therefore, it is preferred that the layer be less thanapproximately 0.001 inches, and more preferably between approximately0.0003 inches and 0.0004 inches. Lubricious coating 120 may be on only aportion of catheter 110 (such as the proximal or distal portion) or thedifferent portions of the catheter can have different lubriciouscoatings thereon.

FIG. 10B shows a cross section of a portion of another catheter 122according to the present invention which includes the lubricous coating120 shown in FIG. 10A. However, catheter 122 simply has braid layer 118sandwiched between two polyurethane encasement layers 124 and 126. Theselayers are preferably formed as described previously in which layer 124is extruded, braid layer 118 is applied, and layer 126 is extrudedthereover. As with the embodiment shown in FIG. 1A, inner lining 120 ispreferably extruded or applied in any suitable way.

FIG. 10C shows another embodiment of the present invention in which aportion of catheter 128 is shown in cross section. Catheter 128 includesa proximal section 130 and a distal section 132. Proximal section 130includes the lubricous inner lining 120 described in the embodimentsshown in both FIGS. 10A and 10B. However, catheter 128 also includes, atproximal section 130, an extruded selective stiffening layer 134 whichis preferably formed of polyimide, polyamide, or polyurethane. The braidlayer 118 is disposed over stiffening layer 134, and a top coat 136 ofpolyurethane or polyamide material is also extruded over braid 118.Selective stiffening layer 134 has relatively high rigidity to providethe proximal section 130 with relatively greater stiffness than distalsection 132.

Between proximal section 130 and distal section 132 is a transitionsection 138. Transition section 138 includes all of the layers describedwith respect to proximal section 130 except that the extrusion ofstiffening layer 134 is tapered off to zero. This provides fortransition section 138 having a rigidity which is intermediate that ofproximal section 130 and distal section 132. Distal section 132 isformed of the same layers as proximal section 130, except thatstiffening layer 134 is no longer present. Therefore, while distalsection 132 is highly flexible, proximal section 130 is relativelyrigid.

The present invention provides means by which a great deal offlexibility can be maintained in the catheter, without sacrificingtorsional rigidity, burst pressure levels, or tensile strength. It hasbeen found that, utilizing the present invention, a preferred ratio ofburst pressure to flexibility is in a range greater than approximately60,000. The present invention has been used to provide shafts with aratio of burst pressure to flexibility in a range of approximately130,000 to in excess of 500,000.

In these examples, burst pressure was measured using a commonly knowntechnique. One end of the shaft to be measured was closed off and theinterior of the shaft was pressurized with a measurable source, until adiscontinuity or fault (such as a hole) developed in the shaft. Thepressure was measured in pounds per square inch (psi).

Flexibility measurements are referred to in terms of the elastic modulus(E) and were taken using a cantilevered method. One end of the shaft washeld in place and the other end was deflected. A measurement of theforce required to deflect the sample beam (or cantilevered shaft) acertain distance was measured. The elastic modulus (E) was calculated asfollows:

E=Fl ³/3I _(z) y  (EQ. 1)

where F=force;

l=the length of cantilever;

I_(z)=the moment of inertia (for a tube I_(z)=π/64 [d₀ ⁴−d_(i) ⁴], whered₀ is the outer diameter of the tube and d_(i) is the inner diameter);and

y=vertical deflection.

For a one half inch length of shaft, the ratio F/y measured was 0.0009pounds per inch of deflection. From this, E can be calculated using theabove equation 1. For example: E=0.0009(0.5³)/3(π64(0.029⁴−0.019⁴))=1324 psi.

Using these techniques, the ratio of burst pressure to flexibility inone preferred embodiment was measured at in excess of 400,000, and hasbeen observed to be as high as 700,000. The shafts used had dimensionsof 0.019 inch inner diameter and 0.029 inch outer diameter. Smallershafts having an inner diameter of 0.012 inches and an outer diameter of0.023 inches have also been successfully manufactured, and the ratios ofburst pressure to flexibility are approximately in the same ranges asindicated above.

The shaft manufactured according to the present invention, includingbraid layer 26, has also been observed to have an elastic modulus in therange of approximately 400 psi to 4,000 psi using standard ASTM elasticmodulus test procedures.

Torsional rigidity or torsional stiffness, as used herein, is determinedas follows:

Torsional stiffness=M/φ=GI _(z) /L  (EQ. 2)

where M=moment;

φ=angle of twist (in radians);

G=shear modulus;

I_(z)=moment of inertia; and

L=length of sample.

To compare different tubes, independent of dimensions, the shear modulus(G) was first calculated using test results. The test included twistingthe sample tube and measuring the moment. The shear modulus can becalculated using the following formula:

Shear modulus=G=ML/φ ^(I) _(z)  (EQ. 3)

To express the relationship between torsional properties andflexibility, the ratio of the shear modulus to the elastic modulus (G/E)was used. The elastic modulus was calculated as set out above. The ratioof G/E for conventional flow assisted catheters is approximately 0.21.The ratio of G/E using the reinforced shaft according to the presentinvention yields a value in excess of 0.25, more preferably above 0.75and has been observed to be in a preferred range above 1.25 andapproximately 1.8-2.6. This is a significant enhancement over prior flowassisted devices.

Another way to express the relationship between burst pressure andflexibility is to express it in terms of a ratio of ultimate hoop stress(σ) and elastic modulus. Using the formula for hoop stress in a cylinderwith uniform internal radial pressure:

σ=qb ²(a ² +r ²)/(r ²(a ² −b ²))  (EQ. 4)

Where

σ=normal stress in the circumferencial direction (hoop stress);

q=unit pressure;

a=outer radius;

b=inner radius; and

r=radius to point (a>r>b).

Using the point OL maximum normal circumferencial stress (r=b) yieldsthe formula:

σ_(max) =q(a ² +b ²)/(a ² −b ²)  (EQ. 5)

Using current methods, the average burst pressure of the tube isapproximately 350 psi and burst pressures as high as 500 psi have beenobserved.

Substituting these numbers into the maximum hoop stress equation 5yields:

σ₃₅₀876.5 lb/in² and

σ₅₀₀=1252 lb/in²  (EQ. 6)

Calculating a modulus for the tube using F/y=0.0009, innerdiameter=0.091 inches, and outer diameter=0.029 inches yields 1324lb/in².

Now calculating the ratio of maximum hoop stress at burst to elasticmodulus (σ_(max)/E), yields:

σ₃₅₀ /E=0.662 and σ₅₀₀ /E=0.946  (EQ. 7)

This can be compared to test results for prior 1.8 French catheters(such as the Balt Magic catheter) in which:

σ_(max) /E=0.15 and

(for the Target Zephyr catheter, assuming 200 psi burst) σ_(max)/E=0.18.

Because incorporation of the braided fiber layers 26 and 56 in the shaftprovide a significant increase in torsional rigidity (and thus torquetransfer characteristics) the treating physician can break any frictionwhich develops between the shaft and the vessel wall. This convertsfriction in the system from static friction to lower dynamic frictionwhich results in further and more smooth tracking.

Because the braid fibers are formed of a number of filaments, the fiberslay down on the tubular surface over which they are braided to provide athin braid band. This increases the surface coverage of the shaft overwhich the braids are disposed, but maintains the wall thickness of theshaft within desirable limits. This improves burst characteristics.Further, braiding provides the shaft with a relatively low elongationpercent (relative to prior flow directed catheters) resulting in lessballooning or radial expansion of the shaft during use.

Also, since torsional rigidity and strength are significantly enhanced,without sacrificing flexibility, the catheter according to the presentinvention can be made with an inner diameter significantly larger thanprior art catheters. The present invention allows satisfactory operationof catheters with an inner diameter of in excess of 0.015 inches and upto approximately 0.021 inches and preferably in a range of approximately0.018 inches to 0.019 inches. This allows greater flexibility in thetypes of injectate, agents, or particles (including coils) which can beadministered with the catheter.

Further, while the reinforcing layer according to the present inventionhas been disclosed in the form of a braided layer, it can also take theform of a tightly wound coil, a mesh sleeve, tapered longitudinalstrands, or similar reinforcing configurations incorporated into thecatheter.

Finally, it should also be noted that the shaft according to the presentinvention may be hydrophilically coated. Hydrophilic coating on theshaft reduces friction between the shaft and the vessel wall and thussignificantly improves the ability of the shaft to flow in the vesseland track through tortuous vasculature. Placing the hydrophilic coatingon the shaft also increases skin drag. Because the coating absorbs waterfrom the blood, it creates a layer of fluid and blood around the outersurface of the shaft that has zero velocity. This increases skin dragand assists in catheter advancement.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. A catheter, comprising: a manifold; a proximalshaft portion coupled to the manifold; and a distal shaft portioncoupled to a distal end of the proximal shaft portion and being flexiblerelative to the proximal shaft portion; wherein the distal shaft portionincludes a pre-shaped curve at a distal end of the distal shaft portionto assist the catheter in being guided by fluid flow.
 2. The catheter ofclaim 1 wherein the distal shaft portion has a longitudinal axis andwherein the pre-shaped curve has a curvature, with reference to thelongitudinal axis of the distal shaft portion, in a range ofapproximately 10°-360°.
 3. The catheter of claim 1, wherein thepre-shaped curve includes an inner curvature and an outer curvature. 4.The catheter of claim 3 wherein the pre-shaped curve inner curvature isconcave, creating a cup-like surface that increases the ability of thedistal shaft portion to be pulled along by the fluid flow.
 5. Thecatheter of claim 3 wherein the pre-shaped curve outer curvature isconvex, creating a rounded, smooth surface that reduces a tendency tosnag or catch along the vascular wall as the distal shaft portiontravels in the direction of fluid flow.
 6. The catheter of claim 1wherein the pre-shaped curve is cut into the distal shaft portion.
 7. Aflow assisted catheter, guidable by fluid flow within a vessel, thecatheter comprising: a proximal shaft portion; and a distal shaftportion coupled to the proximal shaft portion; wherein the distal shaftportion is formed within a pre-shaped curve at a distal end, the distalend being flexible enough to be guided by the fluid flow.
 8. The flowassisted catheter of claim 7 and further comprising: a flexible tipportion, coupled to a distal end of the distal shaft portion, theflexible tip portion being more flexible than the distal shaft portion;wherein the flexible tip portion is coupled to the pre-shaped curve, thepre-shaped curve resiliently holding its shape while maintaining theflexibility of the flexible tip portion.
 9. The flow assisted catheterof claim 8 wherein the pre-shaped curve includes a first surfacegenerally facing the proximal shaft portion and a second surfacegenerally facing the direction of fluid flow.
 10. The flow assistedcatheter of claim 9 wherein the first surface is shaped to increase dragin the direction of fluid flow.
 11. The flow assisted catheter of claim9 wherein the second surface is shaped to reduce impediments to travelof the pre-shaped curve in the direction of fluid flow as the distalshaft portion contacts a wall of the vessel.
 12. A catheter including anelongate member having a lumen extending between a proximal end and adistal end of the elongate member, the elongate member comprising: aproximal shaft portion; a distal shaft portion coupled to the proximalshaft portion; and a pre-shaped curve on a distal end of the distalshaft portion of the elongate member; wherein the pre-shaped curve islarge enough to improve movement of the distal shaft portion through avascular vessel under influence of fluid flow through the vessel.